All questions of Air Pollution for Civil Engineering (CE) Exam

Isokinetic Sampling for SPM Sampling in Chimney Flue Gas

Isokinetic sampling is used for sampling of the flue gas in a chimney for SPM (Suspended Particulate Matter) measurement. It is a widely used method for the measurement of particulate matter emissions from stationary sources.

Working Principle:

The principle of isokinetic sampling is based on the concept of maintaining the velocity of the sampled gas constant. This is done to ensure that the particles in the sampled gas are captured accurately and representatively. The sampling rate is adjusted to match the velocity of the gas in the chimney, which is determined by measuring the gas velocity using a pitot tube or other velocity measurement device.

Procedure:

The isokinetic sampling procedure involves the following steps:

1. Determination of the gas velocity in the chimney using a pitot tube or other velocity measurement device.

2. Selection of the sampling location in the chimney based on the gas velocity.

3. Adjustment of the sampling rate to match the gas velocity.

4. Collection of the sample in a filter holder.

5. Weighing the filter before and after sampling to determine the concentration of SPM in the flue gas.

Advantages:

Isokinetic sampling has several advantages, including:

1. It ensures accurate and representative sampling of flue gas.

2. It is widely accepted and recognized as a standard method for particulate matter sampling.

3. It can be used for a wide range of particulate matter concentrations.

4. It is a cost-effective method for particulate matter measurement.

Conclusion:

Isokinetic sampling is a reliable and accurate method for sampling of the flue gas in a chimney for SPM measurement. It is widely used in the industry and is recognized as a standard method for particulate matter sampling.

Understanding Aerosols
Aerosols are tiny particles or droplets suspended in the air. They can be in different physical states, including solid and liquid. The distinction is important when classifying aerosols, as they have varying impacts on health, environment, and engineering applications.
Different Forms of Aerosols
- Fume: This is typically a solid aerosol, formed from the condensation of vaporized metals or other materials. Fumes are generally composed of very fine particles and are not considered liquid.
- Dust: Dust consists of solid particles that are often larger than those in fumes. It is primarily composed of soil, pollen, or other solid materials and does not fall under the liquid category.
- Mist: Mist is a liquid aerosol formed from tiny droplets of water suspended in the air. This is the correct answer as it represents a liquid form of aerosol. Mist can occur naturally (like fog) or be artificially generated (like in humidifiers).
- Smoke: Smoke is a complex mixture of gases and solid particles produced by the incomplete combustion of organic matter. While it contains liquid droplets, it is primarily classified as a solid aerosol due to its particulate nature.
Conclusion
In summary, among the options provided, mist is the only liquid form of aerosol. Understanding these classifications is crucial in various fields, including civil engineering, where aerosol behavior can affect air quality and material performance.

a) 5: Rainfall is classified as acidic if its pH is less than or equal to 5. This option is correct.

b) 6.5: A pH of 6.5 is considered slightly acidic but does not meet the criteria for classifying rainfall as acidic. Therefore, this option is incorrect.

c) 7: A pH of 7 is considered neutral, and rainfall with a pH of 7 is not acidic. This option is incorrect.

d) 7.5: A pH of 7.5 is slightly alkaline and does not meet the criteria for classifying rainfall as acidic. Therefore, this option is incorrect.

Incomplete burning of wood leads to the production of mainly carbon monoxide (CO) gas.

Explanation:

Incomplete combustion occurs when there is not enough oxygen present during the burning process. In the case of burning wood, incomplete combustion can occur if the fire is not hot enough, if there is not enough air flow, or if there is too much fuel and not enough oxygen. Incomplete combustion of wood releases a number of gases, including carbon monoxide (CO), carbon dioxide (CO2), water vapor (H2O), and other volatile organic compounds (VOCs).

Carbon monoxide (CO) is a toxic gas that is produced when there is not enough oxygen present during combustion. Carbon monoxide is odorless, colorless, and tasteless, making it difficult to detect. In high concentrations, carbon monoxide can be deadly. Carbon monoxide is produced when wood is burned incompletely because the carbon in the wood does not fully combine with oxygen to form carbon dioxide.

Conclusion:

In conclusion, incomplete burning of wood leads to the production of mainly carbon monoxide (CO) gas, which is a toxic gas that can be deadly in high concentrations. Therefore, it is important to ensure complete combustion of wood by providing enough air flow and maintaining a hot fire.

B) 10

c) 100

d) 1000

X-ray films are a source of NO2 gas

Explanation:
X-ray films are commonly used in medical imaging to capture images of internal structures of the body. These films are typically made of a plastic base coated with a gelatin emulsion containing silver halide crystals.

When X-rays pass through the body and interact with the film, they cause a chemical reaction in the silver halide crystals. This reaction results in the formation of metallic silver, which is then developed and fixed to create the final image.

During the development process, various chemicals are used to enhance the visibility of the image. One of these chemicals is nitric acid, which is commonly used as a developer in X-ray film processing. Nitric acid is a strong oxidizing agent and can oxidize the silver halide crystals, converting them into metallic silver.

As nitric acid is used in the development process, it can release nitrogen dioxide (NO2) gas. Nitrogen dioxide is a reddish-brown gas with a pungent odor. It is a highly reactive gas and can contribute to air pollution. In the context of X-ray film processing, the release of NO2 gas may occur as a byproduct of the chemical reactions taking place during the development of the film.

Therefore, the correct answer to the given question is option C) NO2. X-ray films can be a source of nitrogen dioxide gas due to the use of nitric acid in the development process.

Dynamic precipitator is used in ceramic industries.

Explanation:
Ceramic industries involve the production of ceramics, which are non-metallic solid materials that are typically made from clay and other raw materials. These industries often generate dust and other particulate matter during various processes such as grinding, crushing, milling, and drying. To control the emission of these particulates and ensure the production area remains clean, various air pollution control devices are employed.

One such device used in ceramic industries is the dynamic precipitator. Here is a detailed explanation of its working principle and advantages:

Working principle:
1. The dynamic precipitator is an electrostatic air cleaner that removes particles from the gas stream using the principle of electrostatic precipitation.
2. The gas stream containing particulates is passed through an ionization section, where corona discharge electrodes emit electrons that ionize the gas molecules.
3. The ionized gas molecules create a cloud of charged ions and electrons, which then interact with the particles in the gas stream.
4. The charged particles are attracted to oppositely charged collection electrodes, while the clean gas passes through.
5. The collected particles form a layer on the collection electrodes, and periodic rapping or shaking removes them, allowing continuous operation.

Advantages of dynamic precipitator:
1. High collection efficiency: Dynamic precipitators are highly efficient in removing particulates, even those with very small particle sizes.
2. Low pressure drop: These devices have a relatively low pressure drop, resulting in minimal energy consumption.
3. Continuous operation: The periodic rapping or shaking of collection electrodes allows continuous operation without frequent shutdowns for cleaning.
4. Versatile applications: Dynamic precipitators can handle a wide range of gas volumes and particulate concentrations, making them suitable for various ceramic industry processes.
5. Cost-effective: These devices offer long service life and require minimal maintenance, making them cost-effective solutions for air pollution control in ceramic industries.

In conclusion, the dynamic precipitator is used in ceramic industries to control particulate emissions and maintain a clean working environment. Its efficient particle collection, low pressure drop, continuous operation, and versatility make it a preferred choice for air pollution control in this industry.

The primary air pollutant that is formed due to incomplete combustion of organic matter is carbon monoxide (CO). When organic matter such as fossil fuels (coal, oil, and natural gas) or biomass (wood, crops, and agricultural waste) is burned in an environment with insufficient oxygen supply, incomplete combustion occurs, leading to the formation of carbon monoxide.

Incomplete combustion happens when there is not enough oxygen available to fully react with the carbon in the fuel. Instead of producing carbon dioxide (CO2), which is the desired end product of complete combustion, carbon monoxide is formed. Carbon monoxide is a colorless and odorless gas that is highly toxic to humans and animals.

**Formation of Carbon Monoxide:**
During the process of incomplete combustion, the carbon in the organic matter combines with only one oxygen atom instead of two, forming carbon monoxide. The chemical equation for this reaction can be represented as:

C + O2 -> CO

In this equation, C represents carbon, O2 represents oxygen, and CO represents carbon monoxide.

**Sources of Incomplete Combustion:**
Incomplete combustion can occur in various sources, including:
1. Vehicles: Inadequate air supply in the engine can lead to incomplete combustion in vehicles, especially those with older or poorly maintained engines.
2. Industrial Processes: Certain industrial processes that involve the burning of fossil fuels or biomass may produce carbon monoxide if there is insufficient oxygen supply.
3. Residential Heating: Incomplete combustion can occur in households that use wood-burning stoves, fireplaces, or other heating appliances that do not provide enough oxygen for complete combustion.
4. Wildfires: During wildfires, the burning of vegetation can result in incomplete combustion and the release of carbon monoxide into the atmosphere.

**Health and Environmental Impacts:**
Carbon monoxide is a poisonous gas that can have severe health effects on humans and animals. When inhaled, it binds to hemoglobin in the blood, reducing its ability to transport oxygen throughout the body. This can lead to symptoms such as headaches, dizziness, nausea, confusion, and in severe cases, it can be fatal.

In addition to its health impacts, carbon monoxide is also an air pollutant that contributes to the formation of smog and can contribute to the greenhouse effect and climate change. It reacts with other pollutants in the atmosphere to form ground-level ozone, which is harmful to human health and the environment.

**Conclusion:**
The primary air pollutant formed due to incomplete combustion of organic matter is carbon monoxide. It is important to ensure proper combustion conditions and adequate oxygen supply to minimize the production of carbon monoxide and reduce its harmful impacts on human health and the environment.

Sound Intensity Expression

The correct sound intensity expression with usual notations is given by:

a) dB = 10 log10(I/I0)2

Explanation

- The unit of sound intensity is watts per square meter (W/m²).
- The threshold of hearing, I0, is the minimum sound intensity that can be detected by the human ear, which is approximately 1 x 10^-12 W/m².
- The sound intensity level (SIL) is measured in decibels (dB), which is a logarithmic scale that compares the sound intensity of a given sound to the threshold of hearing.
- The formula for SIL is given by:

SIL = 10 log10(I/I0)

- However, since SIL can be negative, it is common to use the formula:

SIL = 20 log10(I/I0)

- This formula is equivalent to the first formula, but it doubles the value of the logarithm to ensure that SIL is always a positive value.
- Therefore, the correct sound intensity expression with usual notations is:

dB = 10 log10(I/I0)2

- This formula is equivalent to:

dB = 20 log10(I/I0)

- Both formulas are commonly used in practice.

Conclusion

The correct sound intensity expression with usual notations is dB = 10 log10(I/I0)2, which is equivalent to dB = 20 log10(I/I0). This formula is used to measure the sound intensity level (SIL) in decibels (dB) by comparing the sound intensity of a given sound to the threshold of hearing (I0).